Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares
Outstanding at beginning of period (in shares)	12,558	23,231	37,495
Exercised (in shares)	(3,901)	(9,842)	(12,662)
Forfeited or expired (in shares)		(831)	(1,602)
Outstanding at end of period (in shares)		12,558	23,231
Vested and expected to vest at end of period (in shares)	8,657
Weighted-Average Exercise Price
Outstanding at beginning of period (in usd per share)	$ 14.77	$ 14.21	$ 13.77
Exercised (in usd per share)	14.77	13.45	12.97
Forfeited or expired (in usd per share)		14.77	13.76
Outstanding at end of period (in usd per share)		$ 14.77	$ 14.21
Vested and expected to vest at end of period (in usd per share)	$ 14.77
Weighted-Average Remaining Contractual Term, Vested and expected to vest	12 days
Aggregate Intrinsic Value, Vested and expected to vest	$ 117

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Number of options outstanding, including both vested and non-vested options.

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-Publisher FASB
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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted-average exercise price, at which grantee can acquire shares reserved for issuance, for fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of share options (or share units) exercised during the current period.

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